1. Field of the Invention
The present invention relates to a process control device and a process control method for control of process steps in which high precision processing is applied to a lot. More particularly, the present invention relates to a process control device and a process control method for control of at least two process steps that are applied to the same lot, before the lot is completed, at the same processing part having a plurality of processing devices placed in parallel therein.
2. Description of the Background Art
In manufacture of various kinds of semiconductor devices such as DRAMs, it is often the case that one process step is performed by a plurality of processing devices placed in parallel with one another to increase production efficiency. In such a process step, each processing object (hereinafter, referred to as xe2x80x9cworkpiecexe2x80x9d or xe2x80x9clotxe2x80x9d) for which a preceding process step has been completed is successively allocated to one of the plurality of processing devices that is currently available. If this process step is of the kind that requires extremely high precision processing, like a photolithographic step, processing results often vary even if the same mask is used under the same processing conditions. This is due to subtle differences in lens property or spectral distribution from a light source of respective processing devices, which are integrated to produce variation in the processing result. For the semiconductor devices such as DRAMs, miniaturization of products have been drastically advanced, and processing devices have reached their limit in capability. Such variation in the processing results according to the processing devices would cause considerable variation in product characteristics, and it would further increase a proportion of the products for which the processing should be done again (hereinafter, a xe2x80x9credo ratexe2x80x9d). This hinders the improvement in productivity.
A proposal has been made to suppress such variation uncontrollable by processing conditions. It states that, if a workpiece is of the kind that is subjected to identical processing more than once at a processing part having a plurality of processing devices provided in parallel therein, the workpiece should be processed by the same processing device in such process steps (Japanese Patent Laying-Open No. 6-168865). Respective processing devices exhibit subtle deviating inclinations specific thereto, which may appear in different directions. For example, assume that a stepper _A tends to deviate a resulting pattern to the right as a whole, whereas a stepper _B will deviate it to the left at large. Applying the steppers _A and _B to the same workpiece will lead to a serious problem. Specifically, if an interconnection and a contact hole are formed using different steppers of which one exhibits an inclination to the right and the other to the left, the interconnection and the contact hole that should overlap will be separated from each other, hindering implementation of a circuit. There may also be a case where two interconnections that should be separated will overlap with each other. On the contrary, if the same workpiece is processed using the same processing device in the identical processing at different steps, such subtle deviating inclination unique to the processing device is always in the same direction, and thus, it is possible to limit the variation in a fixed range. The method as proposed is effective when it is applied to a photolithographic process step during manufacture of a semiconductor device. If each workpiece is processed by one and the same photolithographic device, variation will be suppressed, and good product characteristics will be readily obtained.
The manufacturing steps, however, of the semiconductor device are complicated. The above-described photolithographic process steps, for example, are repeated twenty to thirty times through the entire processing. Therefore, when two or more lots arrive at a particular processing device at the same timing, the lot(s) may have to wait before being processed even if there is another processing device not in use. Thus, the good product characteristics had to be set off by low production efficiency.
An object of the present invention is to provide a process control device and a process control method for control of processing steps of workpieces in which at least two process steps are applied to the same workpiece at a processing part having a plurality of processing devices placed in parallel therein, that ensure good product characteristics while maintaining high production efficiency.
The process control device according to an aspect of the present invention is a process control device for control of a first process step for processing workpieces sorted into a lot and a second process step for further processing the lot processed in the first process step performed at the same processing part having a plurality of processing devices placed in parallel therein. The processing control device includes: a device group information storing unit for storing information about grouping of the processing devices into a plurality of device groups; and a device group selecting unit for selecting the device group such that the lot is processed in the second process step by a processing device included in the same device group as a processing device used in the first process step.
With such grouping of processing devices, it is unlikely that lots waiting to be processed cluster around a single, specific processing device. This prevents degradation of production efficiency. A lot is processed in identical processing at different steps by any of the processing devices belonging to the same device group. Thus, variations attributable to deviating inclinations of processing devices are prevented from appearing in a wide range extending to the right and to the left. As a consequence, it is possible to obtain good product characteristics and also to maintain high production efficiency since the same process steps need not be done again. Note that xe2x80x9ca processing device included in the same device group as a processing device used in the first process stepxe2x80x9d in the above description includes the very processing device used for the first process step.
In the process control device according to the one aspect described above, the device group selecting unit may include a corresponding-device-group-name storing unit that stores the name of the device group corresponding to a lot.
By storing the name of the device group corresponding to the lot, the second process step is reliably performed by a device group the same as that for the first process step. Note that the action to store the name of the device group corresponding to a lot may also be expressed as xe2x80x9cto hold the device group namexe2x80x9d in the description below.
In the process control device according to the one aspect described above, the device group information storing unit may store the grouping of the device groups that is predetermined such that the processing devices having identical deviating characteristics are grouped into the same group.
The expression reading xe2x80x9cthe processing devices having identical deviating characteristicsxe2x80x9d means that the processing results of the processing devices appearing on the lots exhibit identical deviating characteristics; for example, the patterns formed tend to deviate to the right, not to the left, as a whole. As the processing devices that are likely to produce the similarly deviating processing results belong to the same device group, variation attributable to the deviating inclinations of the devices can be restricted. If the processing device is a stepper, steppers that tend to make the patterns deviate to the right as a whole are put into one group, and steppers that are likely to make the patterns deviate to the left as a whole are put into another group. In other words, the steppers exhibiting deviating inclinations to the right and those exhibiting deviating inclinations to the left are not grouped into the same device group. As a result, even though the patterns for the interconnection and the contact hole are formed at different stages using different steppers, if the steppers belong to the same device group and tend to deviate the patterns to the same direction as a whole, it is possible to have an interconnection and a contact hole overlapping with each other as desired. If such grouping is not done, the interconnection pattern and the contact hole pattern may be formed using two steppers having deviating inclinations to the opposite directions. In such a case with the conventional technique, the interconnection and the contact hole that should be overlapped will separate from each other. In addition, according to the conventional art, interconnections that should be separated when seen as a plane may overlap with each other. By conducting the grouping according to the present invention as described above, it becomes possible to obtain good product characteristics while avoiding degradation of production efficiency due to multiple lots gathering around one stepper.
In the process control device according to the one aspect described above, the device group information storing unit may store a target number of lots to be processed. This number is assigned to each device group.
The target number of lots is used as an index of frequency by which lots are actually to be allocated to each device group. Therefore, if a certain device group needs mending so that the number of lots to be processed therein has to be decreased, or if the group currently has a large amount of workpieces, then it is possible to set the target number of lots for that device group smaller than that for another device group. Such target number of lots for a device group may be included in the reference information, or an operator may manually input it based on the in-process information or the like. The target number of lots for a device group may literally be the number of lots. Alternatively, it may be a ratio or proportion of the group to the whole groups regarding the target number of lots to be allocated thereto, or, an inter-group allocation ratio of the target number of lots. Note that the target number of lots to be processed does not need to correspond to the processing capability of each device group, as described above.
In the process control device according to the one aspect described above, the target number of lots may be the number of lots that can be processed in a unit time by each device group.
By recognizing the processing capability of the device group, it is possible to allocate lots to device groups, prior to the first process step, corresponding to their processing capabilities. Thus, the load of processing can be allocated to each device group in balance with its processing capability, whereby the entire production efficiency is improved. Further, the failure rate can be reduced and durability can be improved for each processing device.
The process control device according to the one aspect described above may include: a target-number-of-lots storing unit for storing the target number of lots; an actual-number-of-processed-lots detection unit for detecting the number of lots that have actually been processed by each device group; and an inter-group lot allocation determination unit for determining, prior to the first process step and according to the detection result of the actual-number-of-processed-lots detection unit, which device group processes a lot at the first process step, such that the number of lots being processed by each device group becomes equal to the target number of lots for the group.
By recognizing the past processing performance of each device group at the time point where the lots are to be processed, it is possible to find the difference between the actual number of processed lots and the processing capability of the device group, so that the lots can be allocated to correct such imbalance. Therefore, the load of processing can be distributed to each device group corresponding to the processing capability thereof, preventing the processing from being concentrated onto a particular device group. Thus, high production efficiency can be maintained. The target number of lots may be altered as required. If, for example, a device group encounters an emergent situation in which a mask should be changed, a device is broken, or the number of workpieces has suddenly increased, the above-described inter-group lot allocation ratio for the group can be set to a smaller value or even zero for a prescribed time period. As this ratio serves as an index for lot allocation, the number of lots being allocated to the device group becomes very small. Thus, the lots can be allocated to respective device groups corresponding to their substantial processing capabilities that change according to the situations. In addition, if the target number of lots is equalized with the maximum number of lots that can be processed by each device group within its processing capability, the load can be distributed corresponding to the capability of each group. This helps improve durability of the processing devices.
The process control device according to the one aspect described above may further include a lot transport unit that transports a lot to a location where the device group designated by the inter-group lot allocation determination unit is placed.
With such a lot transport unit, lot processing may proceed smoothly. Note that the location where the device group is placed refers to, for example, a storage cabinet (shelf) that is placed in association with a representative processing device that is designated for the device group.
The process control device according to the one aspect described above may include: a priority determination unit that determines priority in processing order of the lots waiting to be processed by a device group; and a lot selecting unit that selects, according to the priority, a lot to be processed next by a processing device that has finished processing of another lot, and subjects the lot to the processing.
With such configuration, it is possible to minimize the time period in which a processing device is not in use. In addition, each product can be manufactured taking its circumstances into consideration. As a result, a product can be manufactured with flexibility according to its circumstances, such as necessity thereof, with product characteristics being improved and high production efficiency being maintained. Note that the above-described priority may have different criteria for different processing devices. Specifically, the priority for some processing devices may be in compliance with the arrival order of lots at the location where the device group is placed. For other processing devices, the circumstances of the products, such as the necessity thereof, may be given priority over the lot arrival order as above.
The process control method according to another aspect of the present invention is a process control method for control of a first process step for processing workpieces sorted into a lot and a second process step for further processing the lot processed in the first process step performed in the same processing part having a plurality of processing devices placed in parallel therein. The process control method includes the steps of: storing information about grouping of the processing devices into a plurality of device groups; and selecting a device group such that the lot is processed in the second process step by a processing device included in the same device group as a processing device which performed the first process step.
With this control method, lots waiting to be processed are prevented from concentrating onto a particular processing device, whereby degradation in production efficiency is avoided. A lot is subjected to identical processing at different steps using any of the processing devices in the same device group. Therefore, it is possible to restrict the deviation, resulting from deviating inclinations specific to respective processing devices, in one direction. As a consequence, good product characteristics can be obtained. In addition, the redo rate of the same process step is decreased, and thus, high production efficiency is maintained. Note that xe2x80x9ca processing device included in the same device group as a processing device which performed the first process stepxe2x80x9d in the above description includes the very processing device which performed the first process step.
In the process control method according to the another aspect described above, the step of selecting the device group may include the step of storing the name of the device group corresponding to the lot.
By holding the name of the device group corresponding to the lot, it is ensured that the processing devices in the same device group are used for, e.g., photolithography processing.
In the process control method according to the another aspect described above, the device group may be formed in advance such that processing devices having identical deviating characteristics are grouped into the same device group.
With such control method, variation in product characteristics can be restricted by limiting the deviation resulting from inclinations specific to respective processing devices in one direction. Therefore, good product characteristic can be obtained, and high production efficiency is guaranteed with reduction of the redo rate. As described above, the concept of the xe2x80x9ccharacteristics of a processing devicexe2x80x9d includes a structural factor, such as deviation in a fixed direction of a pattern manufactured by a stepper.
In the process control method according to the another aspect described above, the device group may have a target number of lots to be processed that is allocated to each device group.
The target number of lots for a device group is an index of frequency by which lots are actually to be allocated to each device group. Therefore, if a certain device group currently has many workpieces, then the target number of lots for the device group is set smaller than that of another device group. With such setting, lots can be allocated to each device group according to the substantial processing capabilities of the processing devices that change with time. Thus, high production efficiency is maintained. Such target number of lots of each device group may be included in the reference information. Alternatively, an operator may manually input the number based on the work-in-process information or the like. The target number of lots may literally be the number of lots, or it may be an inter-group allocation ratio of the target number of lots.
In the process control method according to the another aspect described above, the target number of lots may be the number of lots that can be processed in a unit time by each device group.
By recognizing the processing capability of each device group, it is possible to allocate lots to device groups, prior to the first process step, for example, corresponding to their capabilities. Therefore, the load of processing can be distributed to device groups in balance with their processing capabilities, which improves the entire production efficiency. In addition, the failure rate can be reduced and durability can be improved for each processing device.
The process control method according to the other aspect described above may include the steps of: storing the target number of lots; detecting the number of lots having actually been processed by each device group; and determining, prior to the first process step and according to the result of the detecting step, which device processes a lot at the first process step, such that the number of lots being processed by a device group becomes equal to the target number of lots for the group.
The target number of lots for a device group as explained above can be changed as necessary. Specifically, if an emergent situation occurs in a certain device group, such as a need to change a mask, breakdown of a device, or a sudden increase in workpieces, the inter-group lot allocation ratio for the group can be set to a smaller value or zero for a prescribed period of time. As this ratio serves as an index for lot allocation, the number of lots being allocated to the device group becomes very small. Thus, it is possible to allocate lots to device groups corresponding to their substantial processing capabilities according to the situations. Further, the lots are allocated to the device groups based both on the processing capability of each device group and on the number of lots that have already been processed therein at the time point where the lots are to be processed, as described above. Therefore, the load of processing can constantly be maintained in balance with the processing capability of each device group. As a consequence, lots waiting to be processed are prevented from clustering around a specific device group. Further still, the number of lots having actually been processed by each device group is recognized at the time of lot distribution, as described above. Thus, the lots can be allocated to correct any imbalance between the load distribution and the processing capability of each device group. Accordingly, it is possible to distribute the load of processing to each device group corresponding to its processing capability. The concentration of processing onto a specific device group is avoided, and high production efficiency is maintained. Durability of processing devices is also improved.
The process control method according to the other aspect described above may further include the step of transporting a lot to a location where a device group designated by the inter-group lot allocation determination unit is placed.
With such a lot transporting step, the processing of lots may proceed smoothly, and high production efficiency is maintained. Note that the location where a device group is placed is specifically a place where a storing cabinet (shelf) is placed corresponding to a representative processing device designated for the device group.
The process control method according to the other aspect described above may include the step of determining priority in processing order of lots waiting to be processed by a device group; and the step of selecting, according to the priority, a lot to be processed next by a processing device which has finished processing of another lot.
With such configuration, the time period in which a processing device is not in use can be minimized, and each product can be manufactured corresponding to its circumstances, such as necessity thereof. As a result, products can be manufactured with flexibility corresponding to their individual circumstances, with product characteristics being improved and high production efficiency being maintained. The priority described above may have different criteria for different processing devices. Specifically, the priority for some processing devices may be in compliance with the arrival order of lots at the location where the device group is placed. Other processing devices may assign higher priority to individual circumstances of each product, such as necessity thereof, than to the lot arrival order as described above.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.